Since the advent of the solenoid driven valve, fluid system designers have continued to design more and more complex systems which take advantage of the computer and remote-controllability of these valves. While early designs often required electric power of a given polarity to be continuously applied to the solenoid to maintain the armature of the valve in a given position, continuing developments soon reduced the amount of power required to be applied to the solenoid valve during such holding periods from that which was required to actually initiate and actuate the valve to that given position. Such a reduced holding power configuration greatly improved the efficiency of the systems which utilized such solenoid valves, especially in systems which required several, possibly in the hundreds, of these valves for proper system operation. While such held valves reduced the overall power consumption required by solenoid actuated valves, and while such held valves provided an additional safety feature that allowed them to automatically close (or open depending on the topology) upon loss of electric power, these held valves are not appropriate for installations which do not include a continuous supply of electric power from a utility.
In many remote locations the installation of an electrically held valve is not practical for various reasons, either because utility power is not available at the installation site, or because the routing of electric power to the particular valve locations is problematic or simply inconvenient. In these types of installations, the use of a latching-type valve is preferred. A latching type valve is one that once actuated to a given position, will maintain the valve state in that position without the further application of electric power. The construction of these latching type valves typically includes a permanent magnet and a spring. Both the spring and the permanent magnet are utilized to maintain the current state of the valve in a particular position.
During one position, the spring force is utilized to maintain that position without the necessity for a holding current to be applied to the solenoid. Once actuated to the other position, the magnetic force of the permanent magnet is sufficient to maintain the armature of the valve in the other position, also without the requirement for additional energy to be supplied to the solenoid to maintain that valve position.
The valve is transitioned between these two positions by energizing the solenoid with electric power of one polarity to move the armature to a first position, and of the opposite polarity to move the armature back. The power required must be sufficient to overcome the spring force to move the armature from the "spring held" position to the "permanent magnet held" position, and must be sufficient to overcome the magnetic force of the permanent magnet to move the armature from the "permanent magnet held" position to the "spring held" position. In this way such a valve requires no electric power to maintain the current status of the valve, it only requires a pulse of electricity through the solenoid of a given polarity to transition the value from one state to the other.
While many configurations of such valves exist, an advanced design of such a valve is illustrated in FIG. 5, and is the subject of co-pending application Ser. No. 05/942,924, filed Oct. 2, 1997, and assigned to the assignee of the instant application, the teachings and disclosure of which are hereby incorporated by reference. As may be seen in this FIG. 5, a plunger assembly 75, comprising plunger 62 and a coil spring 76 disposed within a non-magnetic guide tube 78 (for example stainless steel), resides above the diaphragm 58. The diaphragm 58 (at the location of the anchoring portion 64) and the plunger assembly 75 (at the location of flange 80 on guide tube 78) are fixably attached to the valve body 12 by means of plate 82 and fasteners 84. Although screws are shown as fasteners 24 and 84, any suitable fasteners may be utilized in the construction of the valve 10. The plunger moves axially and vertically along axis 86 under the influence of a magnetic field which is developed by a coil assembly 87 which surrounds the guide tube 78 of the plunger assembly. Together, the plunger assembly 75 and the coil assembly 87 form a solenoid which is responsible for actuating (opening and closing) the valve 10. The coil assembly 87 comprises a wire wound coil 88, which is wound upon a bobbin 90 and surrounded by coil housing 18. Together, the plunger assembly 75, the coil assembly 87, and the valve formed by primarily valve member 58 and pilot valve member 60 comprise an actuatable value unit which connects the inlet 14 to the outlet 16.
A metallic inner sleeve or pole piece 92 is disposed between the bobbin 90 and the guide tube 78 of the plunger assembly, pressed fit into the C-shaped bracket 22. The pole piece serves to fix the position of the coil assembly within the C-shaped bracket. Above the guide tube 78 is disposed a permanent magnet 94, the axial position of which is adjustable along axis 86 by means of set screw 96 and locking nut 98. Set screw 96 threads into corresponding threads 100 in the C-shaped bracket. Locking nut 98 threads into corresponding threads 102 on the outside of set screw 96. The permanent magnet is attracted to the set screw 96 and thus moves therewith. Bracket 22, having the coil assembly fixedly secured thereto by the pole piece 92 is attached to the plate 82, and hence the valve body 12, by means of fasteners 24.
Operation of this advanced design valve 10 is as follows. When in a closed position, as shown in this FIG. 5, the central portion 68 of the primary valve member (diaphragm) 58 rests on wall 74, and pilot valve member 60 closes the central portion opening 72. The valve is closed because central orifice 56 (outlet) is isolated from the horizontal annular chamber 54 (inlet). A pair of bleed holes 104 are formed in the webbed portion 66 of the diaphragm 58. The bleed holes permit fluid to pass from the chamber 54 to an internal cavity 106 of guide tube 78. As such, in the closed position, pressure is equalized on both sides of the webbed portion of the diaphragm (equal pressures in chamber 54 and cavity 106). The valve is latched in the closed position by means of the coil spring 76 which exerts pressure on the inside of the top end 108 of the guide tube, on one end, and on the top end 110 of the plunger 62.
The valve is opened by momentarily applying a voltage to electrical leads 20 to induce an electrical current in the coil which results in a magnetic field being generated having flux lines parallel to the axis 86. The force of the flux lines is sufficient to overcome the force of the coil spring 76 and the plunger moves upward along axis 86. The valve is latched in the open position by permanent magnet 94 which attracts the top end 110 of the plunger 62 (the force of the magnet on the plunger, at this plunger location, is greater than the opposing force of the spring). Thus, power need not be continually applied to the coil to maintain the valve in the open position.
To close the valve, a voltage (of opposite polarity used to open the valve) is momentarily applied to electrical leads 20 to induce an electrical current in the coil and a resulting magnetic field having flux lines parallel to the axis 86 (though in a direction opposite in polarity to the flux lines generated during the valve opening process). The force of the flux lines is sufficient to overcome the force difference between the permanent magnet 94 and the spring 76, and the plunger moves downward along axis 86. The valve is latched in the closed position by coil spring 78 which forces the pilot valve member into the diaphragm central opening 74 (the force of the spring on the plunger, at this plunger location, is greater than the opposing force of the permanent magnet). Thus, power need not be continually applied to the coil to maintain the valve in the closed position.
While such latching type valves present significant advantages over held type valves, much of the advantage provided by these valves could be lost through the inefficiencies of the conventional driver circuitry used to actuate these valves to their open and closed positions. Specifically, typical latching type valve driver circuits operate by energizing the solenoid for a fixed period of time for both the opening and closing event. The time chosen for the pulse period for the driver circuit is typically selected to ensure actual actuation of the valve, regardless of the particular valve actuation characteristics. That is to say, each latching type valve could have different operating characteristics that would vary the amount of time needed to reliably actuate the valve.
Further, as valves aged, their actuation time could vary. Additionally, the particular installation of the valve itself could also have a bearing on the actuation time required, including the temperature of the environment into which the valve is installed, the viscosity and pressure of the fluid which flows through the value, etc. Since all of these various factors could affect valve actuation time, the typical actuation drive circuit pulses the solenoid for an extended period of time to ensure actuation of the valve under the most adverse, worse case conditions for valve actuation time. While the design of these conventional actuation drive circuits is simple and ensures actuation of the valve, they are not very efficient because they continue to supply electric power to the solenoid of a valve which has already transitioned to its actuated state.
Such inefficiencies were not of great concern until the use of battery power was desired for remote installations of these valves. Since a battery has only a limited supply of energy available, maintaining the actuation pulse to the solenoid beyond the time required to actually actuate the valve solely serves to reduce the life of the battery needlessly, thereby reducing the number of valve actuations before battery replacement is required. Further, as a battery's energy is utilized its output voltage typically droops. This drooping actuation drive voltage adds an additional parameter to the actuation time of the valve. That is to say, as the drive voltage varies, so does the time required to actuate the valve from one position to the other. As the battery voltage continues to drop over time, it becomes desirable to have an indication of such low battery voltage so that reliable actuation of the valve may be maintained in all situations. Unfortunately, conventional monitoring means all dissipate additional energy, which serves to reduce the life of the battery that it is monitoring.
There, therefore, exists a need in the art for a new and improved valve driver circuit which will drive the solenoid of a latching type valve for only as long as is needed to ensure actuation of the valve under varying condition of temperature, fluid pressure, viscosity, and battery voltage. There also exists a need for a new and improved valve driver circuit which utilizes the minimum monitoring circuitry to allow such operation so as to not adversely affect battery life. Additionally, there exists a need for such a driver circuit which is capable of indicating a low battery condition without utilizing conventional sense of circuits which also tend to reduce battery life.